Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$68.67	8.432%	$74.4603	$74.46	$74.45	$74.50
Purchase #2	$102.84	9.763%	$112.8803	$112.88	$112.90	$112.90
Purchase #3	$85.49	6.181%	$90.7741	$90.77	$90.75	$90.80
Purchase #4	$156.73	4.389%	$163.6089	$163.61	$163.60	$163.60
Purchase #5	$52.77	12.702%	$59.4728	$59.47	$59.45	$59.50
Purchase #6	$31.43	11.458%	$35.0312	$35.03	$35.05	$35.00
Purchase #7	$134.30	13.539%	$152.4829	$152.48	$152.50	$152.50
7 purchase totals =	$632.23		$688.7105	$688.70	$688.70	$688.80